Stud welders are known in the art. An upper electrode holds a part which is lowered to engage another part on a lower electrode, and then lifted by an energized magnetic coil to start an arc between the parts, followed by spring biased driving force pushing the upper electrode downwardly such that the parts reengage and weld together. Another type of stud welder uses spring bounce to start the arc. In both types of stud welders, the follow-up force is provided by a compression spring.
A disadvantage of prior stud welders is their inability to weld certain materials, for example brass. It has been found that after the arc-starting lift, the follow-up is too slow, and that the arc begins to disintegrate the brass into zinc fumes before the arc is extinguished by reengagement of the parts. The zinc fumes may inhibit the arc, and when the parts come together there may not be a weld formed.
The present invention provides in combination a magnetic booster coil for supplying additional and faster follow-up force driving the upper electrode downwardly after the arc-starting lift. This faster follow-up enables the welding of materials such as brass which were not weldable with prior stud welders.
Magnetic follow-up is itself known, and has been used in welding systems other than stud welding. For example, percussion welding commonly uses magnetic follow-up force to provide the percussive blow to drive the parts together. However, in percussion welding the arc is not started by lifting the weld head. Instead an arc-starter or nib is provided on one of the parts, and when the parts are brought together a high current is passed through the arc-starter nib causing it to explode and start the arc across the gap between the parts. This requires 50,000 to 100,000 amps, and an exemplary application is the welding of contacts of diameter 0.4-1.125 inch. In contrast, stud welders typically require only 2,000 to 4,000 amps, and an exemplary application is the welding of contacts of 0.1-0.375 inch diameter. Unlike percussion welders, stud welders draw the arc by means of weld head lift, which in turn entails particular structural requirements.
For a further discussion highlighting the differences between stud welding and percussion welding, reference is made to my U.S. Pat. No. 4,162,388. For further reference regarding stud welding, reference is made to the commercially available Nelson NSA-80 stud welder, Instruction and Maintenance Manual dated November, 1970, TRW Nelson Division, 28th Street and Toledo Ave., Lorain, OH 44055. For further background regarding percussion welding, reference is made to: "Percussion Welding" R. F. Manning and J. B. Welch, Welding Journal, Sept. 1960, pgs. 1-5; "Percussion Welding" Metals Handbook, 8th Edition, Vol. 6, Welding and Brazing, pgs. 177-186, prepared under the direction of the ASM Handbook Committee, American Society for Metals, Metals Park, OH., 1971; and "Percussion Welding", Welding Handbook, 6th Edition, Sec. 2, Chap. 27, edited by Arthur L. Phillips, published by American Welding Society, N.Y., 1969. For further background regarding various magnetic follow-up systems reference is made to Welch U.S. Pat. Nos. 2,769,080 and 2,776,362, and Park et al U.S. Pat. No. 2,892,068.